"The witness called 911 because she was concerned for Locklear's safety," Marshall said. "When a CHP officer arrived, Locklear was found seated inside her vehicle, which was partially blocking the roadway."

Because Locklear appeared "disoriented and impaired," she was taken to a local CHP station and drug and alcohol tests were administered, Marshall said. The actress was cooperative.

"Alcohol was ruled out as a factor, but based on the officer's observations, we believe Locklear was under the influence of prescription medication," Marshall added.

Locklear was arrested on suspicion of DUI and being under the influence of a controlled substance. She booked at a local jail around 7 p.m., and released hours later.

The actress's lawyer, Blair Berk, wasn't immediately available for comment. Locklear's publicist had no comment.